The present invention relates generally to wire rope, and more specifically to a multi-layer, contrahelically stranded wire rope, which may be plastic impregnated.
Multi-layer contrahelically laid wire ropes are known to exhibit excellent resistance to axial rotation, especially when the inner rope itself is multi-layer and parallel lay. However, when such wire ropes have a central core strand within the inner rope the wire rope exhibits certain undesired characteristics. These characteristics include the tendency of the core strand to assume a greater portion of the load distribution, often becoming the point of initial rope deterioration and the tendency to stiffen the inner parallel lay rope which in turn produces a sliding motion between the outer and inner ropes. Such sliding causes intermediate rope abrasion, expansion or popping of the core strand or of the inner rope and bird caging or expansion of the outer rope. Further, the radial elasticity of the inner rope is reduced. All these undesirable results of the central core strand tend to produce increased inner rope deterioration which is especially undesirable as such weakening of the entire rope takes place before any deterioration of the outer rope is detectable.
Accordingly, it is an object of this invention to provide a high strength, torque-equalized wire rope.